The subject matter disclosed herein relates to a Ram Air Turbine (RAT) and, more particularly, a partial coarse pitch start RAT with enhanced spring support.
Aircraft often include as standard equipment backup power supplied for use in times of power outage in the form of air driven turbines, which are lowered into the airstream, thereby making use of the relative speed of the aircraft through the ambient air to cause the turbine blades to rotate. The rotation imparted to the blades due to their movement through the air is then used to drive electrical generating gear or to provide hydraulic power to the aircraft hydraulic system during the aforementioned times of power outages. These air driven turbine arrangements typically include Ram Air Turbine governor mechanisms that attempt to control the output rotational speed delivered from the turbines to electrical or hydraulic units that are designed to operate most efficiently at a set or given speed.
In some cases, systems employing a Ram Air Turbine governor mechanism start at coarse pitch (approx 50 to 60 degrees) blade angles to enhance start torque and then shift back to fine pitch (approximately 9 degrees) by virtue of flyweights to maximize full speed performance. These systems may present operational issues, however, in that they include cantilevered springs that may create vibration and sticky operation. Also, starting at full coarse pitch start angles may result in the governor mechanisms staying in coarse pitch at low airspeeds because the maximum speed attainable at coarse pitch may be below the speed where the flyweights have sufficient force to shift the governor back to fine pitch.